Re: shadow flicker

["Steven Caron" <carons(at)gmail.com>]

"...and one sample per pixel (aa setting 0)..."

just like bernard and kim said about threshold being misunderstood this too is misunderstood.

mental ray samples at the corners of a pixel. meaning 4 per pixel not 1. but not always 4 new samples because mental ray can share samples with bordering pixels.

*bracing myself now*

steven

On 6/2/06, André Adam <a_adam(at)49games.de> wrote:

A really nice example covering this problem is a hemisphere mapped with
a clear night sky showing lots of small stars. If the min aa setting is
too broad (and one sample per pixel (aa setting 0) might very well be
too broad), the rays will likely completely miss out certain stars on
certain frames which leads to the stars wildly flickering in animation...


kim aldis wrote:

>I'm not trying to put you down here Bernard but there are situations where
>settings like this aren't good and you should have some idea of what sort of
>image you're rendering before making decisions about aa settings. In some
>shots, messing with threshold won't make any difference at all, raising max
>settings will make little difference unless you bring up the min settings.
>You're right, threshold is largely misunderstood. Let's try and shed some
>light:-
>
>here's something you can try. Get a cube, unit 1. scale it so it's really
>long and really thin - 0.02, 0.02, 35.
>now duplicate it 20 or 30 times and space each cube one unit apart in x. Now
>shift them all back away from the camera so you get a good convergance. Lots
>of thin, parallel lines in the distance, all converging to the vanishing
>point is what you're looking for.
>
>Now mess with the aa settings and pay close attention to the quality where
>the cubes are nearly converging. Try 0,3 and mess with the threshold. Not a
>lot of difference, is there, even if you set the threshold really as low as
>you can get it. In fact, changing the threshold varies not a lot at all.
>
>now compare 0,2 with 0,3. Not much better. And I'll bet if you try 1,2 it'll
>be way better than 0,3. Again, regardless of the threshold.
>
>The point here is that there's a real danger of getting it wrong if you
>start generalising aa settings and don't take into account the kind of image
>you're rendering, as Helen is finding out, since sampling grain is fine
>detail. I just tried something here. Pushing aliaising to 1,2 with default
>threshold gave me better improvement than doubling the sampling size.
>lowering the threshold improved things a bit but nothing worked better - nor
>was faster - than raising the min setting, bringing it closer to the max.
>
>If you really want to see how well - or otherwise - aa is working, turn on
>'view sampling' in the region diagnostic tab. It's most revealing.
>
>-----Original Message-----
>From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of
>Bernard Lebel
>Sent: 01 June 2006 16:23
>To: XSI(at)Softimage.COM
>Subject: Re: shadow flicker
>
>I would definitely use a min of 0 and a max of 3.
>
>Also, what is generally ignored or misunderstood is the treshold. The
>treshold color is a control for how sampling is done. Lower values means
>that sampling occurs with lower contrasts, in other words, the level of
>sampling have more chances of getting closer to the max value. Higher
>treshold means a higher contrasts is tolerated before requiring another
>level of sampling, so less samples may be takne.
>
>I never work with treshold higher than 0.05, and had to go as low as
>0.005 on few occasions. Note that at that point, if the image is detailed,
>you should consider ignoring adaptive sampling altogether and use same min
>and max values. If the image has significant amounts of constant colors
>(like shadow passes, black backgrounds in the likes), then adapative
>sampling is still a viable solution.
>
>
>Lastly, my rule of thumb for the filtering is Gaussian 3/3 for TV output and
>Mitchell 4/4 for film output. Gaussian gives a blurrier sample
>interpolation, which may "conceal" minor imperfections.
>
>
>
>Cheers
>Bernard
>
>
>
>
>On 6/1/06, Helen Bucknall <helen(at)helenbucknall.com> wrote:
>
>
>>Mostly I just use min -1 and max 2. and box filtering 1 or sometimes I
>>use triangle 2 for a softer effect.
>>
>>I output a string of 852 x 480 bmps to my clients and then they mpeg
>>it somehow and wack it up on big plasma screens. They never complain.
>>When they want stills for print I just render a frame out huge
>>(3000+)but leave the antialiasing the same.
>>If it's for telly I do HD res. If it's to be comped with live action I
>>ask what anti aliasing they want.
>>
>>
>>
>>Bernard Lebel wrote:
>>
>>
>>
>>>Samples 20 is a bit low. I generally put 64 as soon as I set up the
>>>shadow map.
>>>
>>>What do you mean with "standard antialiasing"?
>>>
>>>
>>>Bernard
>>>
>>>
>>>
>>>
>>>On 5/31/06, Helen Bucknall <helen(at)helenbucknall.com > wrote:
>>>
>>>
>>>
>>>>OK. I dragged the spotlight in closer to the scene elements and it
>>>>seems to have stopped all the flickering! It wasn't that far away,
>>>>but now it is almost close enough to make my character sweaty. I
>>>>also scaled down my ground plane a tad.
>>>>
>>>>Just using 1024 res and sample 20. And bog standard antialiasing.
>>>>
>>>>So very BIG THANKS to all who replied!
>>>>
>>>>Joe Laffey wrote:
>>>>
>>>>
>>>>
>>>>>On Wed, 31 May 2006, Helen Bucknall wrote:
>>>>>
>>>>>
>>>>>
>>>>>>Is there a way to get shadow map shadows to stop flickering even
>>>>>>when nothing is moving?
>>>>>>
>>>>>>This is what I have tried to no avail.
>>>>>>
>>>>>>On the spot light (cone angle less than 90):
>>>>>>Resolution up ( and down).
>>>>>>Softness up and down.
>>>>>>Samples up.
>>>>>>
>>>>>>None of these make any diference to the flickering.
>>>>>>
>>>>>>On the render panel:
>>>>>>I've played around with the antialiasing and jitter.
>>>>>>On the shadows page I've clicked off rebuild.
>>>>>>
>>>>>>
>>>>>
>>>>>If you view your scene from the light is there an extremely large
>>>>>depth to the objects? In other words, are the closest object to
>>>>>the light and the farthest object from the light extremely far
>>>>>apart? This can lead to ZDepth (used for shadowmaps) presision
>>>>>issues in some renderers.
>>>>>
>>>>>This is often the case if you have a huge ground plane.
>>>>>
>>>>>You may be able to exclude some objects, to help, or make smaller
>>>>>versions that catch shadows.
>>>>>
>>>>>--
>>>>>Joe Laffey                |       Visual Effects for Film and Video
>>>>>LAFFEY Computer Imaging   |     -------------------------------------
>>>>>St. Louis, MO             |       Show Reel http://LAFFEY.tv/?e01274
>>>>>USA
>>>>>
---
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